Method for surface treatment of metal plate and vehicle treated thereby

ABSTRACT

When surface grinding finish for decoration or other purposes is performed by applying a film ( 4 ) to the front surface of a metal plate ( 1 ) that is welded linearly with penetration ( 10 ) from the rear surface side thereof, a plurality of the films ( 4 ) are applied so as not to cover weld lines ( 3 ). In this manner, the metal plate ( 1 ) can be subjected to the surface grinding finish such that an appearance similar to weld marks is not created.

TECHNICAL FIELD

The present invention relates to a method for surface treatment of ametal plate in which a film for decoration or other purposes is appliedto the front surface of the metal plate that is welded linearly withpenetration from the rear surface side and to a vehicle treated thereby.

BACKGROUND ART

In recent years, decoration film materials such as foil tapes andresin-made tapes are applied to the surfaces of various vehiclesincluding mass transportation systems such as train vehicles, buses,trucks, and passenger aircrafts to differentiate them from others and todisplay various information such as sense of the season, famous andhistorical places, landscapes, or advertisements.

Plate-like members can be joined together by placing one on the otherand continuously irradiating perpendicularly the surface of one of theplate-like members with a moving laser beam to heat and melt a regionextending inside the plate opposite to the plate irradiated with thelaser beam. In this case, sufficient joint quality can be ensured bycontrolling the output power or moving speed of the laser beam such thatthe bottom of the formed molten pool does not reach the outer surface ofthe plate opposite to the irradiated plate. However, it is known that aridge-like weld mark is visually prominent in a fold portion formed bythe welding process on the outer surface of the plate-like memberopposite to the irradiated plate-like member. In order to address thisproblem, a technique has already been proposed in which such a weld markis made less prominent by employing, as the opposite plate-like member,a plate-like member having an outer surface grinding polished in advancesubstantially parallel to the direction of a weld line to be formed bythe laser beam. This technique is particularly suitable for non-paintedtrain vehicle body structures and for bodies of buses and trucks. (See,for example, Patent Document 1.)

[Patent Document 1] Japanese Patent Application Laid-Open No.2005-329412.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The vehicle body of, for example, the train vehicle described in PatentDocument 1 is also required to be used for decoration and advertisementpurposes by applying the above-mentioned films such as resin tapes toits outer plate.

To satisfy such a demand, the present inventor has decorated a vehicleby applying a film a, such as a resin tape, to an outer plate b thereofproduced by using the technique described in Patent Document 1, as shownin FIG. 8. However, the inventor has noticed that the surface portionsof the film a which are located on weld lines c described above have anappearance similar to that of a weld mark and that these surfaces arevisually prominent.

In view of the above, the inventor has made various studies and foundthat, even when grinding finish or similar processing is performed toaddress folding, the weld mark-like appearance is formed. This isbecause the surface of the resin tape or the like is a kind of glossysurface and also the outer shape of the outer plate is reproduced on theapplied resin tape. The above problem occurs not only in laser weldingthat causes a weld mark described in Patent Document 1 but also commonlyin arc welding and other welding methods in which penetration from thewelded side reaches the front surface of a metal plate from the rearsurface side.

Based on the above findings, it is an object of the present invention toprovide a method for surface treatment of a metal plate in which a filmis applied such that a weld mark-like visual appearance is not presentand to provide a vehicle treated by the method.

Means for Solving the Problems

To achieve the above object, the present invention provides a method forsurface treatment of a metal plate. The method includes applying a filmfor decoration or other purpose to a front surface of the metal platethat is welded linearly with penetration from a rear surface sidethereof. One feature of the method is that a plurality of the films areapplied so as not to cover a weld line.

On the front surface of the metal plate welded linearly with penetrationfrom the rear surface side thereof, a weld mark is formed along the weldline. However, in the above configuration, the surface treatment such asdecoration is performed by applying the plurality of films so as not tocover the weld line. Therefore, even when the surface treatment throughthe use of the films is performed over a large area including the weldline, the applied films do not cover the weld line. Accordingly, thesurface shape of the metal plate having the weld mark along the weldline is prevented from being reproduced. Therefore, even when thesurface treatment is performed over a large area including the weldline, the applied films do not have a visual appearance similar to theweld mark.

In a vehicle having an outer plate composed of a metal plate that iswelded linearly with penetration from the rear surface side thereof, thesame effect as above can be obtained by performing surface treatment byapplying a plurality of films to the front surface of the metal plateserving as the outer plate so as not to cover a weld line.

In another configuration, an edge of any of the plurality of films, aspace between the edges of any two of the plurality of films, a boundaryline between a transparent portion and an opaque portion, or a boundaryline in a streak pattern is disposed along the weld line. In thismanner, the line-shaped design formed by the edge of the film, the spacebetween the edges of the films, the boundary line between thetransparent portion and the opaque portion, or the boundary line in thestreak pattern allows the weld mark along the weld line on the frontsurface of the metal plate to be made less prominent, whereby dullfinishing or grinding finish can be omitted.

In another configuration, the front surface of the metal plate isdull-finished or grinding polished in a direction of linear welding. Inthis case, although the surface of the weld line portion on the metalplate is exposed or made visible when the film or the opaque portion ofthe film is applied so as not to cover the weld line, the effect ofmaking the weld mark less prominent obtained by dull finishing orgrinding finish is not impaired.

Another aspect of the present invention is a method for surfacetreatment of a metal plate in which decoration or the like is applied toa front surface of the metal plate that is welded linearly withpenetration from a rear surface side thereof. The method ischaracterized in that a pattern having at least sections continuous orarranged in a direction of a weld line and discontinuous in a directioncrossing the weld line is disposed so as to cover both a surface of aweld line portion and a surface of a non-weld line portion of the metalplate, the sections of the pattern being formed such that a differencein one of hue, chroma, and lightness between the section and each of thesurface of the weld line portion and the surface of the non-weld lineportion of the metal plate is larger than a difference in the one ofhue, chroma, and lightness between the surface of the weld line portionand the surface of the non-weld line portion.

In the above configuration, the surface of the weld line portion, thesurface of the non-weld line portion, and the pattern are simultaneouslypresent on the surface of the metal plate. As described above, thesections of the pattern are formed such that the difference in one ofhue, chroma, and lightness between the section and each of the surfaceof the weld line portion and the surface of the non-weld line portion islarger than the difference in the one of hue, chroma, and lightnessbetween the surface of the weld line portion and the surface of thenon-weld line portion. In addition, discontinuous gaps are formed atintervals in the direction crossing the weld line between the sectionsof the pattern which are at least continuous or arranged in thedirection of the weld line. The above large difference is observed insurface portions of the metal plate which are exposed in thediscontinuous gaps between the sections of the pattern. Therefore, notonly in the case in which the surface of the weld line portion islocated below the sections of the pattern, but also in the case in whichthe surface of the weld line portion and the surface of the non-weldline portion are exposed, the difference in hue, chroma, or lightnesstherebetween, i.e., the presence of the weld line, is made less visuallyprominent. This effect is obtained sufficiently when the area ratio ofthe surfaces of the sections of the pattern to the surface of the metalplate is greater than the ratio in one of the hue, chroma, or lightnesstherebetween. The larger the difference between the area ratio of thesurfaces of the sections of the pattern and the ratio of one of the hue,chroma, or and lightness, the larger the effect.

The same effect as above can be obtained in a vehicle having an outerplate composed of a metal plate that is welded linearly with penetrationfrom a rear surface side thereof. Specifically, in this vehicle, apattern having at least sections continuous or arranged in a directionof a weld line and discontinuous in a direction crossing the weld lineis disposed so as to cover both a surface of a weld line portion and asurface of a non-weld line portion on a front surface of the metal plateserving as the outer plate, the sections of the pattern being formedsuch that a difference in one of hue, chroma, and lightness between thesection and each of the surface of the weld line portion and the surfaceof the non-weld line portion is larger than a difference in the one ofhue, chroma, and lightness between the surface of the weld line portionand the surface of the non-weld line portion.

Other objects and features of the present invention will be described inthe detailed description below and the drawings. Each of the features ofthe present invention may be used alone or in various practicablecombinations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustrating a part of a train vehicle accordingto an embodiment of the present invention.

FIG. 2 is a general side view of the train vehicle shown in FIG. 1.

FIG. 3 is a cross-sectional view illustrating the relationship between ametal plate, a film applied thereto, and a weld line in an embodiment.

FIG. 4 is a cross-sectional view illustrating the relationship betweenthe metal plate, the film applied thereto, and the weld line in anotherembodiment.

FIG. 5 is a cross-sectional view illustrating the relationship betweenthe metal plate, the film applied thereto, and the weld line in yetanother embodiment.

FIG. 6 is a cross-sectional view illustrating the relationship betweenthe metal plate, the film applied thereto, and the weld line in stillanother embodiment.

FIG. 7 is a diagram illustrating patterns used in a surface treatmentmethod applied to a metal plate of an embodiment and a vehicle in whichthe metal plate is used as an outer plate of the vehicle.

FIG. 8 is a side view illustrating the relationship between a metalplate with controversial weld marks, a film applied thereto, and weldlines.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1 to 7, embodiments of the metal plate surfacetreatment method of the present invention and a vehicle treated by themethod are described in detail to facilitate understanding of theinvention.

Each embodiment of the invention is a surface treatment method fordecoration or other purposes. Specifically, a tape-like or sheet-likefilm 4 made of resin such as vinyl chloride resin or metal foil isapplied to the front surface of a metal plate 1 that is welded linearlywith penetration from the rear surface side, as shown in FIGS. 3 to 7.In an example shown in FIGS. 1 and 2, the metal plate 1 is used as anouter plate of a train vehicle. Specifically, in this example, aplurality of metal-made skeletal members 2 extending in the lengthwisedirection of a vehicle 20 are placed on one another and welded linearlyto portions of the rear surface of the metal plate 1 which are locatedbetween a window 21 and an entrance door 22. However, the presentinvention is not limited to the above embodiment and is applicable togeneral outer plates of other transportation systems and to any metalplate having any shape and used for any application, such as panels fornon-vehicle use.

The skeletal member 2 shown in FIGS. 1 and 3 to 6 has a hat-likecross-section and is laser-welded to the rear surface of the metal plate1. Specifically, as shown in FIGS. 3 to 6, L-shaped attachment flanges 2a on opposite sides of the skeletal member 2 are brought into contactwith the rear surface of the metal plate 1 and are laser-welded suchthat penetration 10 is formed in the metal plate 1 from its rear surfaceside. In this case, a weld mark caused by “folding,” i.e., the formationof a ridge line on the front surface side along a weld line 3, is formedon the front surface of the metal plate 1, and the weld mark is visuallyprominent. Such a weld mark is formed not only in laser welding and lapwelding but also in a case in which weld penetration proceeds from therear surface of the metal plate 1 but does not reach the front surface.As described above, the weld mark can be made less prominent bysubjecting the front surface of the metal plate 1 to dull-finishing orgrinding finish in the direction of the weld line 3 to obtain a roughsurface that causes irregular reflection, as shown in FIGS. 3 and 4.However, when surface treatment is performed over a large area includingthe weld line 3 by applying the film 4 thereto, the shape of the outersurface of the metal plate 1 is smoothly reproduced on the film 4, sothat the above effect of the roughened surface is impaired. Therefore,an appearance similar to the weld mark is created. This problem can beeliminated by forming the front surface of the film 4 into a roughsurface. However, this is problematic when the smoothness of the film 4after surface treatment is desired to be maintained for decoration,display, and other purposes.

Accordingly, the embodiments, particularly the examples shown in FIGS.1, 3, and 5, are basically characterized in that a plurality of films 4are applied to the front surface of the metal plate 1 so as not to coverthe weld line 3. In this case, a weld mark along the weld line 3described above is formed on the front surface of the metal plate 1welded linearly with the penetration 10 from the rear surface side.However, the opaque films 4 are applied so as not to cover the weld line3, when the surface treatment is performed over a region including theweld line 3. Accordingly, the surface shape of the weld mark on themetal plate 1 is prevented from being reproduced on the applied films 4.

As described above, a weld mark along the weld line 3 on the frontsurface of the metal plate 1 welded linearly with the penetration 10from the rear surface side can be made less prominent by subjecting thefront surface of the metal plate 1 to dull-finishing or grinding finish.However, a weld mark-like appearance may be created when the surfaceshape of the metal plate 1 is reproduced on the applied film 4. However,this can be prevented when the method described above is used.

As described above, various vehicles including mass transportationsystems such as train vehicles, buses, trucks, and passenger aircraftsare decorated by applying film materials such as tape or sheet materialsmade of resin or foil to a large area of their front surfaces todifferentiate them from others and to display various information suchas sense of the season, famous and historical places, landscapes, oradvertisements. According to the above method, this can be achievedwithout the influence of the weld marks along the weld lines 3.Specifically, as shown in FIGS. 1 and 2, in the vehicle 20 or the likein which the metal plate 1 welded linearly with the penetration 10 fromthe rear surface side is used as an outer plate, a plurality of films 4for surface treatment are applied to the front surface of the metalplate 1 serving as the outer plate so as not to cover the weld lines 3.In particular, in the train vehicle 20, a large number of skeletalmembers 2 extending in the lengthwise direction of the vehicle are oftenwelded and joined to the rear surface of the metal plate 1 serving asthe outer plate, as shown in FIG. 1. In such a case, the surfacetreatment method by applying the films 4 is useful.

As described above, the weld marks can be made less prominent bysubjecting the outer surface of the metal plate 1 to dull-finishing orgrinding finish. In such a case, it is desirable to apply a film 4having transparent portions 4 a and opaque portions 4 b such that thetransparent portions 4 a are placed on areas corresponding to the weldlines 3, as shown in the examples shown in FIGS. 4 and 6. Even when thecontinuous film 4 is applied, the irregular reflection effect of thesurface of the metal plate 1 caused by dull-finishing or grinding finishcan be obtained through the transparent portions 4 a. Therefore,although the surface shape of the metal plate 1 with weld marks isreproduced, a weld mark-like visual appearance can be prevented frombeing created without sectioning the film 4.

As shown in FIG. 5, an edge 4 c of the film 4 is disposed along the weldline 3. Although not illustrated, the distance between the edges of thefilms 4 may be reduced such that the gap therebetween is disposed alongthe weld line 3. In FIG. 6, the film 4 is disposed such that a boundaryline 4 d between the transparent portion 4 a and the opaque portion 4 bis disposed along the weld line 3. In these manners, the weld mark alongthe weld line 3 on the front surface of the metal plate 1 can be madeless prominent through the line-shaped design formed by the edge 4 c ofthe film 4 or the boundary line 4 d. In these cases, dull-finishing orgrinding finish can be omitted, and therefore the cost of a product,such as a vehicle, using the metal plate 1 can be reduced. Moreover,when the streak-like boundary lines are disposed along the weld lines 3,the weld marks along the weld lines 3 on the surface of the metal plate1 can be made less prominent through the line-shaped design formed bythe boundary lines without dull-finishing or grinding finish. In thiscase, the film 4 may be opaque, and the streak pattern may be formed bythe difference in color, chroma, or density. Such a film is useful forplaces where a large number of weld lines 3 are arranged in parallel,for example, the portions between the windows 21 and the entrance doors22, as shown in the exemplary embodiment in FIGS. 1 and 2. In some bodystructures, a wainscot panel and a frieze panel have a similar structureto that described above, and therefore, such a film can be effectivelyapplied thereto.

FIG. 7 shows another embodiment. In the surface treatment method of thisembodiment, when the front surface of a metal plate 1 welded linearlywith penetration from the rear surface side is decorated, patterns 11are applied to both the surfaces of weld line portions 3 a and thesurfaces of non-weld line portions 1 a. The patterns 11 include, forexample, group A, group B, group C, group D, group E, and group F asshown in FIG. 7. Each of the above patterns 11 has at least sectionscontinuous or arranged in the direction of weld lines 3 anddiscontinuous in the direction crossing the weld lines 3. The sectionsof each pattern 11 are formed such that the difference in one of hue,chroma, and lightness between the section and each of the surfaces ofthe weld line portions 3 a and the surfaces of the non-weld lineportions 1 a is larger than the difference in the one of hue, chroma,and lightness between the surfaces of the weld line portions 3 a and thesurfaces of the non-weld line portions 1 a. In this manner, the surfacesof the weld line portions 3 a, the surfaces of the non-weld lineportions 1 a, and the patterns are simultaneously present on the frontsurface of the metal plate 1. The sections of each pattern 11 are formedsuch that the difference in one of hue, chroma, and lightness betweenthe section and each of the surfaces of the weld line portions 3 a andthe surfaces of the non-weld line portions 1 a is larger than thedifference in the one of hue, chroma, and lightness between the surfacesof the weld line portions 3 a and the surfaces of the non-weld lineportions 1 a. In addition, discontinuous gaps are formed, at intervalsin the direction crossing the weld lines 3, between the sections of eachpattern 11 which are at least continuous or arranged in the direction ofthe weld lines 3. The above large difference is observed in surfaceportions of the metal plate 1 which are exposed in the discontinuousgaps between the sections of each pattern. Therefore, not only in thecase in which the surfaces of the weld line portions 3 a are locatedbelow the patterns 11, but also in the case in which the surfaces of theweld line portions 3 a and the surfaces of the non-weld line portions 1a are exposed, the difference in hue, chroma, or lightness therebetween,i.e., the presence of the weld lines 3, can be made less visuallyprominent. This effect is obtained sufficiently when the area ratio ofthe surfaces of the sections of the pattern 11 to the surface of themetal plate 1 is greater than the ratio in one of the hue, chroma, orlightness therebetween. The larger the difference between the area ratioof the surfaces of the sections of the pattern 11 and the ratio of oneof the hue, chroma, or and lightness, the larger the effect. Asdescribed above, each pattern 11 is formed such that the difference inone of hue, chroma, or lightness is greater than the difference in theone of hue, chroma, or lightness between the surfaces of the weld lineportions 3 a and the surfaces of the non-weld line portions 1 a. Eachpattern 11 may be formed such that the sections thereof are different indensity, color, or chroma while the above-described difference ismaintained, as in groups C, D, and E.

As has been described, even when the front surface of the metal plate 1is an untreated mirror surface, the weld lines 3 can be made lessvisually prominent, and therefore dull-finishing and grinding finish canbe omitted. Therefore, the same effect as above can be obtained in thevehicle 20 having the outer plate composed of the metal plate 1 weldedlinearly with penetration from the rear surface side thereof.Specifically, the patterns 11 each having at least sections continuousor arranged in the direction of the weld lines 3 and discontinuous inthe direction crossing the weld lines 3 are disposed so as to cover boththe surfaces of the weld line portions 3 a and the surfaces of thenon-weld line portions on the front surface of the metal plate 1 servingas the outer plate. The sections of each pattern 11 are formed such thatthe difference in one of hue, chroma, and lightness between the sectionand each of the surfaces of the weld line portions 3 a and the surfacesof the non-weld line portions 1 a is larger than the difference in theone of hue, chroma, and lightness between the surfaces of the weld lineportions 3 a and the surfaces of the non-weld line portions 1 a.

The patterns 11 described above may be formed by applying film materialssuch as tape or sheet materials or by applying a coating.

INDUSTRIAL APPLICABILITY

When the front surface of a metal plate having linear weld marks issubjected to surface treatment by applying a film thereto, a visualproblem may occur in which the shape of the metal plate with the weldmarks is reproduced on the applied film. According to the presentinvention, the visual problem can be avoided.

1. A method for surface treatment of a metal plate (1), comprisingapplying a film (4) for decoration or other purpose to a front surfaceof the metal plate welded linearly with penetration (10) from a rearsurface side thereof, wherein a plurality of the films (4) are appliedso as not to cover a weld line (3).
 2. The method for surface treatmentof a metal plate according to claim 1, wherein the front surface of themetal plate (1) is dull-finished or grinding polished in a direction oflinear welding.
 3. The method for surface treatment of a metal plateaccording to claim 1, wherein an edge (4 c) of any of the plurality offilms (4), a space between the edges (4 c) of any two of the pluralityof films (4), a boundary line (4 d) between a transparent portion (4 a)and an opaque portion (4 b), or a boundary line in a streak pattern isdisposed along the weld line (3).
 4. The method for surface treatment ofa metal plate according to claim 3, wherein the front surface of themetal plate (1) is dull-finished or grinding polished in a direction oflinear welding.
 5. A method for surface treatment of a metal plate (1),comprising applying a film (4) for decoration or other purpose to afront surface of the metal plate welded linearly with penetration (10)from a rear surface side thereof, wherein: the front surface of themetal plate (1) has been subjected to dull-finishing or grinding finishin a direction of linear welding; the film (4) includes a transparentportion (4 a) and an opaque portion (4 b); and the film (4) is appliedsuch that the transparent portion (4 a) is disposed on an areacorresponding to a weld line (3).
 6. A vehicle comprising an outer platecomposed of a metal plate (1) that is welded linearly with penetration(10) from a rear surface side thereof, wherein a plurality of films (4)are applied to a front surface of the metal plate (1) so as not to covera weld line (3).
 7. The vehicle according to claim 6, wherein the frontsurface of the metal plate (1) serving as the outer plate isdull-finished or grinding polished in a direction of linear welding. 8.A vehicle comprising an outer plate composed of a metal plate (1) thatis welded linearly with penetration (10) from a rear surface sidethereof and has a front surface that has been subjected todull-finishing or grinding finish in a direction of linear welding,wherein a film (4) including a transparent portion (4 a) and an opaqueportion (4 b) is applied to the front surface of the metal plate (1)such that the transparent portion (4 a) is disposed on an areacorresponding to a weld line (3).
 9. A method for surface grindingfinish of a metal plate (1) in which decoration or the like is appliedto a front surface of the metal plate that is welded linearly withpenetration (10) from a rear surface side thereof, wherein a pattern(11) having at least sections continuous or arranged in a direction of aweld line (3) and discontinuous in a direction crossing the weld line isdisposed so as to cover both a surface of a weld line portion (3 a) anda surface of a non-weld line portion (1 a) of the metal plate (1), thesections of the pattern (11) being formed such that a difference in oneof hue, chroma, and lightness between the section and each of thesurface of the weld line portion (3 a) and the surface of the non-weldline portion (1 a) of the metal plate is larger than a difference in theone of hue, chroma, and lightness between the surface of the weld lineportion (3 a) and the surface of the non-weld line portion (1 a).
 10. Avehicle comprising an outer plate composed of a metal plate (1) that iswelded linearly with penetration (10) from a rear surface side thereof,wherein a pattern (11) having at least sections continuous or arrangedin a direction of a weld line and discontinuous in a direction crossingthe weld line is disposed so as to cover both a surface of a weld lineportion (3 a) and a surface of a non-weld line portion (1 a) on a frontsurface of the metal plate (1) serving as the outer plate, the sectionsof the pattern (11) being formed such that a difference in one of hue,chroma, and lightness between the section and each of the surface of theweld line portion (3 a) and the surface of the non-weld line portion (1a) is larger than a difference in the one of hue, chroma, and lightnessbetween the surface of the weld line portion (3 a) and the surface ofthe non-weld line portion (1 a).